Although unlikely, it is possible that during operation of a gas turbine engine a rotating airfoil can fail by separating from the hub or disc and being released in a radial direction. A surrounding containment structure is designed to capture the released airfoil and prevent it from leaving the engine, in either the radial or axial direction. The containment structure must be strong, and for airborne applications, lightweight. It is also desirable, of course, to provide components as cost effectively as possible. A turbofan fan case is one example of an airfoil containment structure, and a compressor or gas generator case is another example. In addition to performing a containment function, a gas generator case is also a pressure vessel.
Traditionally, a fan case is manufactured by machining a forging, but this wastes much material, and requires several steps, and therefore time. Traditionally, a gas generator case is machined out of two or three forged or sheet metal rings, provided to meet the various thickness requirements and design intents, then these rings are welded together. However, the weld joint(s) must to be located in a region away from the fragment trajectory of the impeller blade, since weld lines are not desired in containment sections of components. All these steps are time consuming and therefore increase lead-time. It is desirable to provide improved ways for manufacturing annular gas turbine engine cases in effort to reduce lead-time and manufacturing costs.